The Bratcam gets a Mitutoyo tube lens

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Chris S.
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The Bratcam gets a Mitutoyo tube lens

Post by Chris S. »

In a recent thread, I listed components for incorporating a Mitutoyo tube lens into a macro setup. The list drew on ideas of mine and Charlie Krebs. I’ve since built the assembly described in that thread, so here it is.

The tube lens in its assembly:

Image


Here is the tube lens assembly mounted on the Bratcam. Since the assembly has a Chris Hejnar Arca Swiss compatible rail for a base—as do my bellows and macro lenses—any of these can be interchanged quickly with the quick-release clamp:

Image


Parts labeled (the lettering is kept consistent with the earlier post—so it may seem a bit strange, here):

Image

All stock numbers and prices are Edmund Optics, US dollars as of February, 2011, unless otherwise indicated:

A.) Mitutoyo MT-1 tube lens: (Stock number NT54-774, $628). This lens has a focal length of 200mm, and when used with a Mitutoyo (or, I presume, Nikon) infinite objective, provides the magnification rated for the objective. A Mitutoyo MT-2 lens is also available, with a focal length of 400mm, which doubles the objective’s magnification. These are not to be confused with the MT-4/MT-40 tube lenses, which are described as “designed for end-user integration,” and appear to be of more limited application.

B.) MT-1/MT-2 C-mount adapter: (Stock number NT58-329, $159). This is a two-part adapter designed specifically for the MT-1 or MT-2 tube lenses. The tube lens is mounted inside this adapter (see photos later in post) and provides standard C-mount threads on both sides. Note that this adapter has a slightly larger diameter than a T-tube, so the T-tube ring mounts (parts I) can not be placed around it.

C.) Mitutoyo to C-mount 10mm adapter: (Stock number NT55-743, $33). This is a short tube with, on one end, a male C-mount thread to screw into part B, and on the other end, a female M26 x 0.706 mm (26 TPI) thread to accept a Mitutoyo objective. Users of Nikon infinite objectives should note that while this adapter may work for them, the Nikon M26 thread pitch is slightly different—0.75mm.

D.) Male T-Mount to Female C-mount adapter: (Stock number NT58-753, $39). This is for the camera side of the tube lens—bumps the thread size up to T-mount, which permits a wider tube for convenient mounting and to avoid vignetting. The junction between parts D and E is not visible in the photo, as it is covered by the ring mount (part I).

E.) T-Mount Extension tube 100mm: (Stock Number NT52-296, $33). Provides appropriate additional tube length and convenient support.

F.) 35-60mm T-mount Fine Focus Tube: (Stock number NT52-300, $71.00). I have this cranked out a few millimeters so that the tube lens (without objective) focuses at infinity. There is a set screw on this tube that can be tightened to lock the tube after adjustment. I find that it must be locked down for rigidity. Since the Nikon flange focal distance is 46.5mm vs. Canon’s 44mm, a Canon shooter would want to crank this part out 2.5 additional mm. Other camera types would of course differ.

G.) T-mount to Nikon F-mount adapter: Free to me, because I have several, but about $15 online. Canon or other brand shooters would obviously use their appropriate camera mount, here.

H.) Arca-Swiss rail from Chris Hejnar (not an Edmund part—about $40). This came from my box of rails, and had ¼-20 inch threaded holes, which Don Wilson, of Wilson’s Welding & Fabricating, bored out and countersunk in order to accept flat head screws. These screws go from the underside of the rail, up through the rail and into the T-mount rings (parts “I”). (For those who wonder why I had the threads bored out, be aware that directly attaching two parts having threaded holes, via a threaded screw, doesn’t work very well—the two parts will tighten to an orientation that is almost surely not the one you want. So the screw must be freely turnable in the base rail.)

I.) T-Mount 48mm Ring Mount with ¼-20 tapped hole: (Stock number NT52-304, $65). There are two of these in the rig.




Pictures of the Mitutoyo tube lens and holder are scarce, so here are some of mine.

1 Parts B (left) and A (right)—that is, the C-adapter and tube lens. The brass rings partly visible inside the C-adapter are shims for use with the MT-2 tube lens, and not used in this assembly.

2 Same as above, seen from the side.

3 Here with the end of the C-adapter removed, exposing three screws that will hold the tube lens.

4 Here with the tube lens screwed into the end of the C-adapter.

Image


Below is an Edmund Optics Mitutoyo filter holder (Stock number NT56-993, $69). This holder has Mitutoyo M26 threads on both ends, and so goes nicely between the tube lens assembly and objective. In it I placed a 25.4mm diameter Edmund Optics Techspec High extinction Linear Glass Polarizing Filter (Stock number NT47-316, $135). It has a high extinction factor and is very color neutral—and so works well for cross-polarization. As an alternative to this expensive filter, Edmund Optics stock number NT54-926 might be a usable alternative at much lower cost—$23.00—but the specifications are not as good. It would also be possible to mount a polarizing filter in a short C-mount tube with appropriate retaining rings, and place this tube between parts A and C.

Edit: For this filter holder, the combination of the inner threads and the retaining ring that screws into them leaves a 3mm gap at the tightest adjustment. Despite the fact that Edmund optics descibes this filter holder as "compatible" with polarizing filters," the polarizing filter is only 1mm thick. This left the polarizer a bit loose, with 2mm of "jiggle room." While this did not seem to present an optical problem in test shots, it still bothered me, as I don't like having optical elements move randomly in an assembly. However, the addition of a 0.49$ USD hardware-store O-ring has nicely cured this issue. The O-ring has an outer diameter of 26mm and a thickness of 2mm. (A similar 1-inch O-ring was surprisingly a bit too loose.) After the addition of the O-ring, the polarizing filter is now very snug. Thanks to Rob T. at Edmund Optics tech support for helping me work this out.

Image


Here is the assembly with the filter holder and my longest infinite objective, the Mitutoyo Plan Apo 50x. Despite the fact that the lens is cantilevered pretty far out into space, it is steady in test stacks. That said, I’ll probably add additional support, if only because it bothers me to have things sticking out into the air unsupported.

Image


How well does it work? My quick answer is “very well”—but I have not done rigorous testing. After a number of trial stacks, I have not found it wanting. Before, I was mostly using the Nikon 200mm f/4 ED-IF micro lens to decollimate the Mitutoyo objectives. While the Nikon lens did work for Mitutoyo objectives from 2x through 20x, my sense was that it didn’t equal David Millard’s apo lenses intended for large format. That said, I doubt we can truly compare results by different photographers with different subjects and lighting. Interestingly, when using the Nikon micro lens for decollimation, I was never able to get a remotely sharp image with my pickiest objective, the Mitutoyo Plan Apo 50x. With the Mitutoyo tube lens, getting decent results with the 50x is easy.

Also, I think an important test for a decollimation lens is how it performs with the objective spatially separated from it. This spreads out the light waves a bit, which tends to use less optimal portions of the decollimation lens. This is important if one wishes to use a filter, beam splitter, or other apparatus between objective and tube lens. With the Nikon lens used to decollimate, I could not get useful images with a polarizing filter adapter in place. But with this tube lens setup, I can.

Here is a quick test shot with the Mitutoyo Plan Apo 50x (208 images @ 1 micron, Zerene Stacker PMax). Subject is Uraneus ripheus; for amusement, I wanted the shot to include both shiny scales and dark scales, which challenges the dynamic range of my sensor and workflow.

Image


Another quick shot—same objective, same subject, different spot—and this time with cross-polarization. While it may appear a bit less sharp than the above image, I don’t think it really is—the effect seems to be caused more by the harsher direct lighting necessitated by x-pol. (146 images @ 1 micron, Zerene Stacker PMax.) This and the above shot could definitely use some retouching, but these were meant to be very quick demonstrations. Also, I realized after the fact that I did not flock the inside of the filter holder—something I should definitely do. This might have introduced some flare.

Image

A very important note: This assembly desperately—desperately—required flocking. I used Protostar material for this, flocking every possible surface. This made an immense difference in performance.

Things I may change:

1. I purchased, and may add, a C-Mount 30mm Ring mount with ¼-20 tapped hole: (Stock number NT52-930, $65). This is similar to the ring mounts for the T-tubes (parts I), but for smaller C-tubes. I would have to add a short C-tube extension between parts A and C, as part C is not wide enough to occupy the ring mount without interfering with the objective. I don’t think I really need this, but as mentioned above, I have some discomfort in having the objective on such a long cantilever; that said, if it’s working well at 50x, I probably don’t need it.

2. I think I’ll add an additional ring mount (part I) around part F, or just drill an additional hole in the Hejnar rail and move one of the existing ring mounts. Again, this is probably not necessary, but one can never have too much support.

3. Add a second Hejnar rail to the side of the assembly for vertical camera orientation. Vertical orientation is quite possible now, by slightly loosening the screws that tighten the ring mounts and turning the assembly. But I’m not sure I like that approach—a second Hejnar rail would add rigidity and be quicker.

4. Make a beam splitter to go between objective and tube lens for axial lighting.

5. Make a drop-in filter holder to replace the filter holder I described above. I’d like to be able to rotate a polarizer without changing the position of the threading, and would like to be able to drop in a blue filter after focusing (this would allow me to use short-wavelength visible light for monochrome images, but have the full range of light for focusing).

--Chris

-edited to correct typos (longest infinite objective, not finite), and others
Last edited by Chris S. on Tue Apr 19, 2011 11:06 pm, edited 5 times in total.

Eric F
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Post by Eric F »

Chris,

Splendid presentation -- and much appreciated. Thanks very much,

Eric

Charles Krebs
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Post by Charles Krebs »

=D> I knew you wouldn't wait too long to do this! :wink:

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Post by ChrisR »

Chris,
Splendid presentation -- and much appreciated. Thanks very much, :smt038
Chris

Chris S.
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Post by Chris S. »

Eric, Chris, and Charlie, thanks for your kind words! It's very encouraging to hear that a post like this is considered useful by knowledgeable community members.

And Charlie, you're right--I needed a bit of time to dissipate the sticker-shock on the parts-list, and to try a couple of other approaches that didn't work as well. But this is what I really wanted, and I'm glad now that I have it. And I'm betting that you, like me, get a kick out of seeing something we talked about in PMs come to life?

Cheers,

--Chris

dmillard
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Post by dmillard »

Chris,

Thank you very much for such a clear and comprehensible presentation - It's given me food for thought. :-k

David

Craig Gerard
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Post by Craig Gerard »

Chris,

A streamline assembly.

Thanks for the detailed, well presented and clearly documented information.

The filter holder (NT56-993) ...do Edmunds have an iris that could be incorporated within that piece?


Craig
To use a classic quote from 'Antz' - "I almost know exactly what I'm doing!"

Chris S.
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Post by Chris S. »

David and Craig, you're very welcome! Glad to provide food for thought.
Craig Gerard wrote:The filter holder (NT56-993) ...do Edmunds have an iris that could be incorporated within that piece?
Interesting question. On quick look, I see irises small enough to fit inside that adapter, but their maximum apertures are not large, so I suspect they would vignette.

There is a "C-mount Iris Diaphragm Barrel" (NT03-623, $129) that could be mounted very easily between parts A and C or A and D in my assembly, as it has C-mount threads on both ends. However, it's maximum clear aperture is only 10mm, as compared with the 25.4mm through-bore of the C-tube. Not sure if it would vignette, but suspect it would.

But check out the "T-Mount Iris Diaphragm Barrel" (NT52-299, $99). This appears to have T-tube threads on each side. So it would mount easily between parts D and E in my rig (or for that matter, between parts E and F, but location doesn't see intuitively useful). Would an aperture placed between D & E work well? I don't know. But the 30mm clear aperture would likely be plenty wide.

Alternatively, it would be possible to mount this T-mount iris between tube lens and objective, with appropriate adapters. This is especially appealing, as I've been thinking that having some T-tube bit on the objective side of the tube lens would facilitate beam splitters and drop-in filters.

--Chris

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Post by ChrisLilley »

Chris,

Thanks for once again carefully and clearly documenting your latest addition. The parts list and pricing is particularly helpful as well as the usual clear photographs and discussion.

I have vaguely considered a 'supported extension tube' setup as a bellows replacement, for lenses used at a standard extension such as short-mount tube lenses.

The placement of the length fine-tuning part after the two supports rather than between them seems suboptimal; isn't the camera hanging from that partly-unscrewed portion?

But the quality of the posted photos speaks for the rig as a whole working very well.

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Post by RogelioMoreno »

Chris,

Thank you for the detailed presentation.

Rogelio

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Post by rjlittlefield »

Chris, as I mentioned in PM this is a super job, both the equipment and the post. I'll spend a lot of time re-reading this one!

Regarding any added aperture, it really needs to go close to the objective, where the current aperture is. The farther back the added one goes, the more likely it is to just vignette instead of doing something useful like increasing DOF.

--Rik

Craig Gerard
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Post by Craig Gerard »

Chris.S wrote:Alternatively, it would be possible to mount this T-mount iris between tube lens and objective, with appropriate adapters. This is especially appealing, as I've been thinking that having some T-tube bit on the objective side of the tube lens would facilitate beam splitters and drop-in filters.
Chris, as Rik has already indicated, having the iris diaphragm positioned close to the rear of the objective is important with regard to vignetting.

Edmund Part # NT03-623 might be useful?
Image

When using a Rodenstock Apo-Gerogon 150/9 enlarging lense for a 'tube lense', the distance between the rear element of the objective and the Apo-Gerogon iris is approximately 20mm, so with regard to positioning of the iris, there appears to be some flexibility, to some degree.

Working in the area you've indicated "on the objective side of the tube lens" is the most appropriate location for an iris, that being the 'area of system expandability' for an infinity based setup.
http://www.nikon.com/about/technology/c ... /index.htm

Regarding the beam-splitter component. About a month ago, a particular item appeared on eBay, the listing included a Mitutoyo 20X M Plan Apo objective, attached to the rear of the objective was a beam-splitter made by Navitar. It was a very tidy, streamline combination. It may be worthwhile perusing the offerings from Navitar for this component and enquire with regard to application.


Craig
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Chris S.
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Post by Chris S. »

ChrisLilley wrote:Thanks for once again carefully and clearly documenting your latest addition. The parts list and pricing is particularly helpful as well as the usual clear photographs and discussion.
Chris, I much appreciate your feedback. I always wonder about how much detail is wanted—so it’s useful to hear that things like part numbers and prices are helpful.

ChrisLilley wrote:The placement of the length fine-tuning part after the two supports rather than between them seems suboptimal; isn't the camera hanging from that partly-unscrewed portion?

But the quality of the posted photos speaks for the rig as a whole working very well.
I fully agree, Chris. I tried to convey this under “Things I may change,” item 2 (and similarly, in item 1):

“2. I think I’ll add an additional ring mount (part I) around part F, or just drill an additional hole in the Hejnar rail and move one of the existing ring mounts. Again, this is probably not necessary, but one can never have too much support.”

The rig does work pretty well right now—but you know how these projects go; as soon as you build something, you see how to improve it. Like other projects, this one is evolving—I’ll probably add additional support at both ends of the current assembly. As you point out, the current stacks don’t seem to indicate a problem. But like you, I keep thinking that the current placement of the ring mounts is suboptimal. Current placement of the ring mounts was dictated partly by the Hejnar rails I had sitting around—there just wasn’t a place to drill a ¼-20-inch hole on the camera side of the fine-tuning part. I’m going to order a third T-tube ring mount, and contact Chris H. about a slightly longer rail without any center cut, then ask Don Wilson to drill and countersink holes exactly where I want them. This third ring mount will go around the “partly unscrewed portion.”

And considering “Things I may change,” item 1: “I purchased, and may add, a C-Mount 30mm Ring mount with ¼-20 tapped hole: (Stock number NT52-930, $65). This is similar to the ring mounts for the T-tubes (parts I), but for smaller C-tubes. I would have to add a short C-tube extension between parts A and C, as part C is not wide enough to occupy the ring mount without interfering with the objective. I don’t think I really need this, but as mentioned above, I have some discomfort in having the objective on such a long cantilever; that said, if it’s working well at 50x, I probably don’t need it.”

I think I will go ahead and order a short C-tube, and use the C-mount ring to further support the objective end. Again, I’m not at all sure this is needed, but adding more support probably won’t hurt, and feels right intuitively.

Rogelio, you’re welcome! (And thanks much for your good words.)

Rik, thanks again for your kind comments (and for correcting my typo in your earlier PM).
rjlittlefield wrote:Regarding any added aperture, it really needs to go close to the objective, where the current aperture is. The farther back the added one goes, the more likely it is to just vignette instead of doing something useful like increasing DOF.
I do understand this in principle; what I don’t know is just how close to an objective an aperture needs to be. Perhaps this is just one of those things that needs to be tested—and perhaps might vary with various objectives? Regardless, I don’t really think that placing an iris between tube lens and camera would be a useful thing—just mentioned it earlier because it was possible to mount it there (and because my two-year-old niece was distracting me--pulling on my arm to take her for a walk and a wallow in a nearby stream :).
Craig Gerard wrote:Edmund Part # NT03-623 might be useful?
Image
Craig, I believe this is the same part I referenced above. The potential problem with it is that it has a maximum clear aperture of 10mm, whereas a standard C-tube has a through bore of 25.4mm—so I strongly suspect even when wide open, it would vignette or impose diffusion constraints on some of my objectives.
Craig Gerard wrote:When using a Rodenstock Apo-Gerogon 150/9 enlarging lense for a 'tube lense', the distance between the rear element of the objective and the Apo-Gerogon iris is approximately 20mm, so with regard to positioning of the iris, there appears to be some flexibility, to some degree.
You provide a very interesting data point, Craig. If 20mm is not a problem, perhaps the following—which I alluded to above, but did not specify part by part, would work OK between tube lens and objective (this is a composite of images current at the Edmund Optics Website 4-11-2011):

Image

X.) Male T-mount to Female C-mount adapter (Edmund Optics NT58-753, $39).

Y.) T-Mount Iris Diaphragm Barrel (Edmunds Optics NT52-299, $99). Iris plane sits 12mm from female end.

Z.) Female T-Mount to Male C-mount adapter (Edmund Optics NT53-483, $39)

This hypothetical assembly seems to place the iris about 24.5 mm (one inch) from the rear of the objective. Might work?

I should point out that including an iris in the assembly is not, at present, on my priority list. I do see how it is useful to soften the ends of a stack with iris-induced diffusion. And I’ve seen that this approach has been deftly applied by talented members of this forum. But my current thought is that this effect may be best handled in the software domain, where it may easily be adjusted without the necessity of reshooting. An approach that seems really appealing is one recently described by Rik, wherein (if I understand it correctly) one approaches a deep stack by first stacking smaller “slabs” (stacked subsets of the total stack), then performing Gaussian blurs on some slabs at the rear (or potentially front) of the total stack, then stacking the slabs. Also, I could easily see writing a Photoshop action (possibly one which calls a script) to progressively blur images at the ends of a stack. So if I find myself seeking this effect, I will likely try it in software before creating a hardware approach—simply because I’d prefer adjusting software parameters to re-shooting, for obtaining a desired final effect.

Craig Gerard wrote:Regarding the beam-splitter component. About a month ago, a particular item appeared on eBay, the listing included a Mitutoyo 20X M Plan Apo objective, attached to the rear of the objective was a beam-splitter made by Navitar. It was a very tidy, streamline combination. It may be worthwhile perusing the offerings from Navitar for this component and enquire with regard to application.
Craig, I went looking at the completed auctions at eBay, hoping to see this item. But apparently, it was long enough ago (I think the cutoff is three weeks?) that it is no longer listed. Too bad—I’d like to have seen it. But I’ll watch for Navitar beam splitters. Beam splitting is not right now on my priority list, but a few excellent posts in the galleries appear to be using them, though if so, I haven’t seen it mentioned.

Thanks, and cheers, all!

--Chris

Craig Gerard
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Post by Craig Gerard »

Chris,

Regarding the beam-splitter. The auction referred to was 250792508477 8)
Navitar model 60255 with right angle 1/2 mirror for fiber optic illumination and C mount adaptor
It was a BIN....it was gone before I received email notification about the listing.... :(


Craig
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Chris S.
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Post by Chris S. »

Craig, that unit does indeed look nice and compact. I’d wonder, though—since that beam splitter is designed for a tube lens that appears to be of smallish diameter, adds considerable magnification, and is likely intended for small sensors--if it would cover a full-sized tube lens and APS camera sensor. I’m not actually planning to add a beam splitter any time soon—I’m just glad to have a rig that can be taken in that direction if the need arises.

Weirdly, without the auction number you supplied, I can’t get that particular auction item to show up in any search of completed listings, regardless of what words I search on. Strange. And based on standing searches I have at eBay, I should have seen this go by, but didn’t. Since I already have a 20x Mitutoyo, I wouldn’t have purchased it, but would certainly have studied the assembly. Thanks for sending the auction number.

--Chris

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